August 12, 1996: Granular materials are a
form of matter that we encounter every day, yet we often fail to appreciate
their many faces in nature. Sand is an excellent example. On an average
day at the beach, we can build a sandcastle, a seemingly solid structure,
yet also pour sand from one bucket to another as easily as we pour a glass
of water. It can act on one hand like a solid, yet on the other like a liquid.

The principal strength of these types of granular materials - whether it's
the soil under your house or the sand under your feet at the beach - is
friction and geometric interlocking of the small particles. If the material
is forced together, it becomes very stiff. For instance, coffee, which is
also a granular material, becomes stiff like a brick when packaged under
vacuum. Conversely, if the material is only loosely held together, it can
be soft, weak, and can even display properties found in liquids such as
flow.

Scientists from NASA's Marshall Space Flight Center in Huntsville, Alabama
are teaming with colleagues from the University of Colorado at Boulder to
study the behavior of these types of granular materials during the upcoming
flight of the space shuttle Atlantis on STS-79.
Their experiment is called the Mechanics of Granular Materials (MGM)
experiment. Scientists are taking advantage of the reduced gravity environment
found aboard the space shuttle to focus on how these materials behave under
very low stresses. On the ground, the earth's gravity can collapse soil
samples under their own weight during these low stress conditions.

The results of these experiments in space may lead to an increase in our
knowledge of a wide variety of subjects, including improved selection and
preparation of building sites, better management of undeveloped land, earthquake
engineering, coastal and offshore engineering, mining, transport and handling
of granular materials such as grains and powders, and soil erosion, which
irreversibly depletes fertile top-soil, to name a few.

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